Metering telephone system



Jail 1 9 F. ALDENDORFF METERING TELEPHONE SYSTEM Filed June 21 7sheets-sheet 1 LA .Q31 E?" H- FL- FF i.

ffl. .Q

fllllviIlIIK im 55H15 JQ@ Aw Jan. 1 7 w24 L479A42 F, ALDENDORFF METERINGTELEPHONE SYSTEM Filed June` 2l 1920 7 Sheets-Sheet 2 Jan.. 1, 1924,479,44Z

F. ALDENDORFF METERING TELEPHONE SYSTEM Filed June` 2l 1920 Sheets-Sheet5 l l l l METERING TELEPHONE SYSTEM Filed June 2l 1920 7 Sheets-Sheet 4,

| lwswl :1991

Jan. 1, 1924 ,479,442

F. ALDENDoRl-v-F AMETERING TELEPHONE SYSTEM Filed June` 2l 1920 '7Sheets-Sheet 5 zzg 1 l6600 asco lV01l Vel Jan. l, 1924 ,479,442

F. ALDENDORFF METERING TELEPHONE SYSTEM Filed June` 21 1920 7sheets-sheet 6 Jan, 1, 1924 1,479,442v

F. ALDENDORFF METERING TELEPHONE SYSTEM Filed June 2l 1920 '7Sheets-Sheet 7 Wrri l `A y LL www Patented .l an. 1,1924.

UNITED STATES Pairlairr OFFICE.

METERING TELEPHONE SYSTEM.

Carved out of application on which Patent No. 1,319,031 was igrantedOctober 14, 1919, and filed after grant of that patent. This applicationled June 21, 1920. Serial No. 390,32011.

(GRANTED UNDER THE PROVISIONS 0F THE ACT 0F MARCH 3, 1921, 41 STAT. L.,1313.)

To all whom it may concern:

Be it known that I, FRITZ ALDENDORFF, a citizen of the `,GermanRepublic, residing at 32 Mannheimerstrasse, Wilmersdorf, Berlin,Germany, have invented'certain new and useful Improvements in MeteringTelephone Systems (for which applications have been filed with myconsent in Germany on the 15th of November, 1913, by the Gesellschaft frelektromechanische Telephonapparate m. b. H., in Berlin-Wilmersdorf, andin England, by Harold Baron, on the 8th of December, 1913, and on whichapplications a German Patent No. 322,248 issued on 26th of June, 1920,and an English Patent No.

28,291 of 1913, was accepted on the 15th of July, 1915), and of whichthe following is a specification.

My invention relates to electromechanical or automatic or semi-automaticswitching systems. It relates more specifically to meter arrangements ina system of the kinddescribed in my application Serial No. 814451, filedJan. 26, 1914, Patent No. 1,319,031. The present application containsthe same disclosure and is filed after the grant of said patent.

An object of the invention is to economize switches. IThis object isattained by providing switches which act according to the requirementsof the moment as line finders or as connectors; in other words theseswitches at times connect a calling line to a free trunk leading toanother switch such as a group selector or connector and other timesthey extend a connection which has advanced to a certain stage to thewanted subscribers connected to subscribers" lines and with a. setofmovable contacts or brushes capable of being brought into contact withany of their sets of fixed contacts. From the set of brushes of each ofthese switches which will henceforth be called two-way switches becausetheyextend connections from calling subscribers to a trunk and at othertimes .from a trunk to a subscriber) one trunk or link circuit leads tothe movable contact arms of a group selector or a selector finder andanother trunk leads to the fixed contacts of a grou selector or selectorfinder. The set of brus ies of each two-way switch is connected Whilstthe switch is in its normal position to the movable contact arm. of thegroup selector or selector finder with which it is associated. But assoon as the two-way switch is to be used for establishing a connectionwith a wanted subscriber its brushes are disconnected from the contactarm of the group selector or selector finder associated with it and areconnected to the trunk extending to the fixed contacts of-the groupselectors or selector finders.

The brushes of some of the two-way switches are directly connected togroup selectors whilst others are connected to group selector finderswhich establish connections with free group selectors.-

The two-way switches are started or set in motion one after the other bystarting impulses sent through a starting circuit in the order in whichthe calls are made by the calling stations.

The moment a subscriber calls the battery lead to the calling or linecircuits of the other subscribers is opened by a call regulator until aconnection is made between the calling subscriber and a group selectoror conL nector. The line relayl of each subscriber has` a lockingcircuit which is closed the moment the subscriber calls in order torender thev calling circuit of this subscriber independent of the commonbattery lead which is opened immediately after the call is made.

Whenever a two-way switch is moved out of its normal position in orderto establish a connection with a calling line the startinor circuit isdisconnected from this switch and is immediately extended to the nexttwo- Way. switch. This also takes place whenever a two-way switch isused for connecting with a wanted line. For these t-wo cases two specialswitches are provided one of which is shifted .bythe two-way switchitself as soon asit is moved out of its normal position, the other beingshifted independentlyof its two-way switch by a current from a groupselector over the trunk leading to the two-way switch.

The starting -circuits of the two-way switches are arranged so that thestarting i of several switches by the same starting impulse isimpossible. This is accomplished by arranging the switch that extendsthe starting circuit from one two-way switch to the next'so that thestarting circuit is ex- I tended only after a starting impulse hasceased owing. The extending switch has a spring which is tensioned by amagnet excited by the starting impulse and which only exerts its :torceso as to shift the extending switch after the starting impulse has.ceased flowing.

In largeexchanges the subscribers lines are divided into groups and eachgroup of lines is connected to a group of two-way switches. The groupsof subscribers lines are sub-divided into sub-groups. Each twoway switchis composed of two finders, a prima and a secondary finder. The primaryder inds the calling line and the secondary inder finds the sub-group inwhich the calling line is contained. In order to hasten the action ofthe two-way switch when finding a calling line its primary and secondaryiinders are arranged to act simultaneously. Permutation wires areprovided for each group .of subscribers which are connected to contactsof all the primary and secondary finders of the group and which, at themoment a subscriber calls, determine the points at which the linders ofthe two-way switch vused for the call shall stop in order to extend thecalling line to a group selector or link circuit. ten sub-groups and tenlines in each subgroup the greatest number of steps to be taken by theprimary and secondary finders will be ten and as both finders actsimultaneously the maximum time required for iinding any particular lineout of 100 is the time that the brushes of a finder take to travel thedistance .occupied by ten adjacent sets of contacts.

YWhen a two-way switch is used to make a connection with a wanted linethe circuits of the motor magnets of the primary and secondary findersof the switch, which are ordinarily connected to a common circuit, areseparated and the motor circuits are then controlled separately by theperson setting up the connection with the aid of a switch controller'.

The primary and secondary motor circuits of a two-way switch areseparated also when restoring the switch to its normal position.

The two-way switches are each provided with two test relays, one for theprimary finder and another for the secondary finder, which open the.circuits of the finder motor ymagnets the moment they find the properpermutation wire. These vtest relays are made inoperative when thetwo-way switch 4is used to connect to a Wanted line.

If there are Another feature of the invention consists in an rimpulserepeater located at a group selector at which impulses arising in oneportion of a circuit are repeated in another portion of the circuit, thesecond portion being normally disconnected by open contacts from thefirst and the open contacts not being closed` until the calledsubscriber in responding to the call changes the strength of the ringingcurrent sent to him from a group selector.

In order to simplify the circuits of the last selector in an establishedconnection (i. e. of the selector or connector that makes connectionwith the wanted line) no circuits are used in this selector which actbackwardly on the impulse repeater at the group selector. A calledsubscriber in responding to a call iniiuences the impulse repeater atthe group selector without the aid of any intervening devices orcircuits placed at the last selector. This is accomplished bytentatively applying a source of ringing current through a ringingcontrol electromagnet or relay located at the group selector to leadsextending through a chain of selectors to the wanted line. Thearrangement of the ringing control circuits is such that if the wantedline is busy and the test relay in the last or final selector is notexcited, no ringing current Hows through the said ringing con,- trolmagnet on account of the ringing current path to the wanted line nothaving been closed by the said test relay. If the line is busy theringing current does not flow. Whether the ringing current remainsconnected to the leads or not is made dependent on its flowingimmediately after it is kconnected to the leads. If the ringing curits'armature until the called subscriber responds to the call and causes astrengtheniing of the ringing current. AWhen the ringing cut-olf relayis thus energized it closes the circuit of a connecting relay whichcloses the contacts that separate the calling half of the circuit fromthe called half and also prepares a meter circuit which is closed vwhenthe connection is broken at theiend of the conversation.

The energization of the ringing cut-olf relay also results, in thecuttingvoif of the ringing current.

The invention is illustrated in the accompanying drawing in which Fig. lShows the "iso ' secutively 3 of the. lower five group selectors,

general connecting plan of the new system. Fig. 2 shows the circuits ofthe subscribers line relays, the arrangement of the permutation or guidewires of the two-way switches and the arrangement of the call regulator.Figs. 3 and 4 illustrate the circuits of the two-way switches whichperform the two functions of connecting a calling line to a groupselector and of connecting a trunk leading from the fixed contacts of agroup selector to a wanted line. Fig. 5 shows the circuits of theselector finders designated HS in Fig. l. Fig. 6 illustrates thecircuits of a first group selector with an impulse repeater and Fig. 7shows the circuits of a second group selector. By placing Figs. 2 to 7beside each other with Fig.' 2 at the left and Fig. 7 at the right end adiagram of the complete system forming the subject of this inventionwill be obtained. Figs. 8 and 9 illustrate certain contacts used in myapparatus.

In Fig. l the three first groups of one hundred subscribers of anexchange for 1000 lines are diagrammatically indicated. To

the right of the bracket I are indicated the switching apparatus VS1,HSI and GWI of the first hundred group. The switching apparatus of thesecond and third hundred groups are shown at the right of the bracketsII and III.

It will be assumed that there are 15 twoway switches (only ten shown) ineach group which in the cases of calls coming from the subscribers S tothe exchange conneet the calling subscribers to free group selectors GIVand in the cases of connections extended by group selectors GW to trunksh1, k2 etc. connect these trunks to the lines of the wanted subscribers.

Each two-way switch VS is shown by three arcs l, 2, 3 and a movablecontact or brush 4. Each arc l, 2, 3 is supposed to represent a row often setsof fixed contacts. In reality each two-way switch has ten rowsof ten sets of contacts in each but to simplify the drawing anddescription only three rows are indicated.

The lines of three subscribers S11, SI2, SIF-Sun SH2: Snai-smi; .Smm SmsConnect* ed to the third contact rows of the twoway switches areindicated.

Of'the l5 two-way switches in each group 5 are connected directly togroup selectors GIV and 10 are connected to group selectors by means ofselector finders HS to any idle one of a group of l5 group selectors.The latter group is made up of 5 groups selectors in each of the threehundred groups.'

The 10 selector finders HSI endeavour to pass calls first to the lower 5group selectors GWI. If these are all busy they test con- GWn and ifthese are busy also they proceed to test 2 ofthe lower 5 selectors GVVm.In asimilar manner the selector finders idle.

HSII test first the lower 5 group selectors GW, then 3 selectors GVS7mand finally 2 selectors GVW. The selector finders HSm test first fiveselectors GWW, then 3 GWI and finally two GWH.-

Of the contact rows of the group selectors only three are indicated bythe arcs p, s, t; eac row of contacts is multiply connected to a trunkcable h, h, which contains the trunk wires leading to the fifteenmovable contacts 4 of the particular group of the two-wayv switches.

The trunk cable lz., leads to the two-way switches VSI of the firsthundred group, the trunk cable k2 to the two-way switches VSII of thesecond hundred and h3 to the switches VS1 of the third hundred etc.

The path of a talking connection through the system will now beillustrated: Suppose a subscriber SI calls. The brush 4 of a disengagedtwo-way switch will immediately move into contact with the line of thecalling subscriber and will connect this line to a group selector. Thisconnection to a group selector GW will be either direct or through aselector finder HSI. The calling subscriber SI or a semi-automaticoperator will now cause the movable contact 5 of the group selector toselect the row of fixed contacts that corresponds to desired hundredgroup e. g. the row leading to the second hundred II that is connectedto the trunk cable h2.

The group selector now hunts automatically for a free two-way switchVSH. When this is found the person controlling the switches causes thebrush 4 of two-way switch VS1I to be'moved into contact'with the wantedsubscribers line,-e. g. SH3.

As the two-way switches VS are used both `A for outgoing connectionsoriginating at the subscribers stations and for incoming connectionswhich come to the subscribers stations from other stations and serve thedouble purpose of line finders and connectors, a considerable saving ofswitches is accomplished.

In the known systems in which separate line finders and connectors areused it will hap en `that all the line finders of a group are usy whilstysome ofthe connectors of the group are still free. Further callingsubscribers would not be able to make connections as .all the linefinders are busy. But in the new system with two-way switches that willdo the work of line finders or connectors accordin of the moment thescribers will still be able to make connections as long as any two-wayswitches are If at any moment the demand for connectors is in excess ofthe demand for to the re uirements f urther ca ling subline finders thisdemand will be supplied made in the busy hour or with the sameconiecting capacity fewer switches can be use Fig. 2 indicates thecircuits of the subscribers of a hundred group. Each hundred grou issub-divided into tensl groups and represent the first two subscribersofh the first tens group, S22, S22 the firsttwo subscribers of thesecond tens group and S131, S32 the first two subscribers of the thirdtens group. ,The other subscribers are omitted in order to simplify thedrawing.

If the subscriber S12 calls, his line 121, 12b must be connected throughthe movable contacts ba, bb, boe-ba1, bb1, b01 of the two-way switch,Fig. 3, to a trunk line va, vb, @c which leads directl or indirectly(through a selector finder HS Fig. 5) to a first group selector GW1. 2

The brushes ba, bb, bc-b1, bb1, b'c1 of the two-way switches VS are setor guided to the positions in which they establish a connection betweenthe trunk ea, vb, 'vc and the calling line (represented in this case bythe contacts KS12) by guide wires or permutation wires pu, pt.

The guide wires are divided into two groups pu, pt one of which guidesthe primary finder to the contact representing the calling line, theother guiding the secondary finder to the contact representing the tensgroup in which the calling line is contained. When a subscriber calls,his line vrelay e. g.

11412 is energized and it earths one wire in each of the groups of guidewires pt and pu thus setting up a circuit combination which will causethe proper motions of the primary and secondary finders of the next freetwoway switch in the particular hundred group for connecting the callingline to a trunk.

'The calling ofthe subscriber S12 i. e. the second subscriber in thefirst tens group results in the contacts 100, 101 of hisline re-A layZ732 earthing the first wire 311 of the tens group of guide wires pt andthe second wire 2.1`of the unitsgroup of guide wires. If the subscriber11v calls his line relay contacts earth the first tens gpide wire Z11and the iirstunitsguide wire Z1. `A call from sub` scriber No. 21 wouldresult in the earthing of the tens wire 211 and the units wire Z1 and soforth, so that a certain combination of earthed guide wires correspondsto each of the hundred subscribers of the group.

In Fi 3 only the circuits of one two-way switch f S is shown but thepermutation or guide wires pt, gm lead to all the two-way switches ofthe hundred group and are connected to each of these switches by branchWn'es w1 we, we', 'wu 'ws-p1- pza 232 Q4 P5' The contact sets les of thetwo-way switches of a grou are`connected in multiple. I

'From t e common call e lator AR of eachgroup 'a starting wirev Wextends to the two-way switch VS. As soon as Lama this switch is takeninto use its starting wire SW is extended through a switch 104 or 103 toan extension starting wire SW#1 which leads to other switches similar to103, 104 on the next two-way switch. If the second two-way switch of thegroup is also engaged the startin .wire is extended to the third two-wayswitch and so forth.

The primary finder of each two-way switch has ten sets of three brusheseach ba, bb, bc and a guiding brush pb, al1 these brushes being drivenso as to brush ast sets of contacts k3 and single contacts lrespectively by a common driving shaft D. If the brushes are moved so asto make the guiding brush pb rest` upon the guiding contact k2, each ofthe sets of brushes ba, bb, bc will yrest upon the second sets ofcontacts las in the row of contact sets 70810, 76820, lasso, etc., thatit rides over. If the brush pb were to be moved to the fourth guidingcontact k2 each of the sets of brushes ba., bb, be would also be movedto the fourth set of contacts los in its particular row and so forth.

The common driving device that moves all the brushes consists of aratchet wheel ZR fixed to a shaftJDwhich is rotated step byA whichwhilst the two-way switch is in its normal position opens the contactsy104, 110-105, 10S- 106, 107 and .closes the con'- tact 104, 108. Themoment the two-way switch leaves its normal position the contacts 106,107-105, 108-104, 110 are closed and the contact 104, 109 is opened.

Only one set of brushes ba, bb, bc will be connected to the trunk ca,ob, v0 when a connection has been extended through the two-v wayswitch.l The set of brushes to be connected to the trunk is selected bythe secondary finder ZW which has ten-sets of fixed contacts Ke of fourcontacts each and a set of ^four movable brushes ba1, bb1, b01, sb. Theset of brushes ba1, bb1, bc1, sb is driven in any suitable manner e. g.by a shaft D1 which is turned "with the aid of a ratchet wheel ZR1 by apawl KL1 oscillated by the' armature Am1 of the secondary finder drivingmagnet ZM.

The chain of events which happen when a 'subscriber calls andestablishes av connection` ulator, thence through 113, 114, 12a, S12,12", 115 to earth. The line relay Z111, at-tracts its armature closes alocking circuit for itself through the contact 116. By closing itscontact 117 the line relay closes the circuit of the call regulator AR(battery B, AR, 117, earth) and this Iattracts its armature and byopening thecontact 112 opens the common battery feeder of all the linerelays of the hundred group to which the calling subscriber belongs, sothat no other subscriber of the same group can make a call by closinghis loop and energizing his line relay until a two-way switch VS hasconnected the first calling subscriber to a group selector.` Theconnecting operation of the two-way switch will, however, not requiremore than about 92 a second so that if the second subscriber callsimmediately after the first the delay in taking up his call will be soshort that he will not notice it. The purpose of the momentary cuttingofi' of the battery feed to -all the subscribers except the first tocall is to prevent a mixing of the calls and a wrong s etting of thetwo-way switches which would be possible if more than one call werepassed on to the two-way switches at a time. For

this reason the sequence in which the callsare passed on over thestarting wire S'W is regulated so that the calls are transmitted overthe starting wire one after the other.

By its contacts 100, 101 the line relay Z132 earths the first tens guidewire Zll and the second units guide wire 2l so that the contacts k2 andzin all the two-way switches of the group will be earthed and the pointsindicated where the brushes sb and sp of the particular two-way switchused are to stop.

rlhe call regulator in attracting its armature causes a momentaryclosure of the contact 119, 120. The armature 118 brushes past thespring 119 and momentarily presses 119 against 120. When the armaturefalls back into its normal position 119 is pressed away 120 and noclosure of contact 119, 120, takes place.

It is thus seen that the moment the subscriber S12 calls-a currentimpulse is sent by the momentary closure of the contact 119, 120 fromthe battery B through SW. If the two-way switch VS is idle this impulsewill fiow through 103, 111, 154, 104, 109, 155, 116, 156 t6 157. A1, chepoint 157 the starting impulse divides into three parts the one partflowing through 131, 158, motor magnet ZM of the secondary nder, 159 toearth and another part throuli 131, 160, 115, 161, 162, motor magnet Eof the primary finder, 163 to earth and the third part through 164,13'5, ah, 200, 201, 203, starting relay to earth. The magnets ZM and EMattract their armatures and each shifts its pawl (kl and loll) into thenext tooth of its ratchetV wheel ZR, ZRl. When the starting impulsethrough contact 119, 120 ceases the pawls k1 and cbl are drawn back totheir normal positions by their springs 165, 166 and the ratchetv wheelsZR,'ZRl are turned one step as a result of which the sets of brushes ba,bb, bc and the brush pb and also the brush set ball, bbl, bol, sb areshifted. The movement of the shaft D out of its normal osition alsocauses the off-normal switch O 1 to be shifted and the first two-wayswitch VS of the group to be cut-off' from the starting circuit 154 atContact 104, 109 and to be connected to an interrupter 168. The startingcircuit 154 is simultaneously extended through contacts 104,110'andthrough SW1 to the next idle two-way switch of the group so thatthe starting impulse caused by the subscriber that calls next will flowthrough the magnets ZM and EM 0f the next idle two-way switch.

The motor magnets of the started twoway switch will now be energized bycurrent impulses which flow from the negative pole of the exchangebattery through 168, 105, 108, 155, 118, 156, ,157, 131, 158, ZM, 159 toearth and through 131, 160, 115,

161, 162, EM, 163 to earth respectively. As

soon as the brush pb reaches the' contact k2 of the second units guidewire 2l which is earthed by the armature contact 101 a c urrent willflow through the test relay pr from the negative pole through 117,169,134, 170,

.moved at the same time as the brush sets ba, bbc, be and as soon as thetest brush 8b strikes'the tens guiding contact al which is earthed bythe armature contact 100, a current will flow through the secondary testrelay sr from the negative pole through 117,`

169, 134, 170, 8f, 174, 8b, pl, zu, 173, 100 t6 earth. This willenergize the secondary test relay which will open motor magnet circuitthus causing the set of brushes bwl, bbl, bcl, sb to stop at the firstcontact set Ica.

In the case assumed in which the twelfth subscriber of the hundredgroupis calling the circuit of the secondary finder magnet will beopened immediately after the starting impulse has flowed, because themoment this impulse ceases the brush set bal, bbl,

bel, sb will be advanced to the first set ofcontacts'kaof the secondaryfinder.

The first contact set Ica is connected to 'the' first set of brushes ba,bb, bo counting from the right, so that the calling subscriber S12 willnow-be connected through am, bn, 012, 70812, the first set of branchesba, bb, be, the first contact set las, brush set bal, bbl, bol

.to the trunk fva, fvb, Ivo.

regarded in connection with the line nding The moment the test ,relayspz, sz are both energized, the contacts 132, 133 will be closed and acurrent will liow from the negative pole through 132, 133, 125,connecting relay tz, 124 to the positive pole. The relay tz closes itscontacts 141, 142, 143 and thus extends the wires fva, fvb, fvo to thewires zal, p51, zal. The relay tz also closes and opens a number ofother contacts, but these are only of importance when the two-way switchis used as connector and need not be operation of the two-way switch.

It was mentioned above that the starting relay 205 of the selectorlinder HS, Fig. 5, was energized at the same timeas the motor magnets EMand SM by the starting impulses sent through .the starting wire SW atthe moment the subscriber S12 called. When the relay 205 is energizedthe contacts 202, 203 are opened and the contacts 204, 208, 207 closed.By its contact 204 the relay 205 closes a locking circuit for itselfwhich is independent of the starting circuit ah and may be traced fromthe negative pole through 213, 204, 205 to earth. By its contact 208 therelay 205 closes the circuit of test relay pzh and by its 207 thecircuit of the turning or motor magnet 206 of the selector finder(negative pole, interrupter 218, 210, 206, 207, earth). The turningmagnet 206 now rotates the brushes wa, wb, wc by a ratchet and pawlarrangement in a wellC known'manner causing them to brush over the fixedcontacts connected to the trunks fvaz, p52, p02, until an'idle trunk isreached. A current then flows from the negative pole through 208, 211,pzh, we, 002, relay ez, 219 to earth. The relays pzh and ez areenergized. The relay pzh opens the circuit of the motor magnet 206 atitscontact 210 so that the brushes wa, wb, we stop on the xed contactsconnected to the trunk paz, wb2, l00 leading to an idle first selectorGWI. y its contact 212 the test relay closes a locking circuit foritself which is independent of the contact 208 and at its contact 213 itopens the circuit of the starting relay 205. By its contacts 214, 215,216 the test relay extends the line of the calling subscriber to thefirst group selector GWI. The relay pzh opens the contact 217 andthereby prevents a premature release impulse from flowing from the earththrough 209, 202 to the release wire al. By the opening of contact 200unnecessary oscillations ofthe armature of the starting relay areprevented which would be caused by impulses flowing from the interrupter168 through 108155, 118, 156, 164, 135 and ha.

When the callin line is extended to-the group selector by the closure ofthe contacts 214, 215,216 the cut-olf relay ozu, of the callingsubscriber is energized by a current owing'from the 'positive pole ofthe battery the trunkwa2, wb2, 'U02 will now not receive sullicientcurrent to energize them so that the trunk fm2, wb2, zo, will appearengaged.

By the energization of the cut-off relay cz12 the line relay zu is cutoil' from the calling line. On the deenergization of the line relay Zzmthe earth connections of the guide wires 111 and 21 are removed and atthe same time the call regulator AR is deenergized by the opening ofcontact 117. When the call regulator is deenergized it does not closethe contact 120, 119, but it reconnects the battery B to the contacts112 of all the line relays Zz of the group so that the call of the nextsubscriber will now be taken and passed on to the next idle twowayswitch.

The time that elapses from the moment the subscriber calls to the momentwhen the two-way switch VS and the trunk selector HS have establishedthe connection between the calling subscriber and the group selectoronly amounts to a fraction of a second so that the likelihood of twocalls waiting to be taken up is extremely remote and if it occurs thesecond.'v subscriber to call will not notice any delay.

As soon as the earth connections of the guides wires 111, 21 are removedthrough the cutting oil' of the line relay Zz12 the circuits of the testrelays pz, sz will be broken and the contacts 163, 159 in the circuitsof the motor magnets EM and ZM will be closed. But these circuits willnow be kept open at the contact 131 of the connecting relay tz.

It has been said'that when the brushes wa, wb, we are caused to stop onthe idle trunk fvaz, wb2, '002, relay ez is energized that is associatedwith this trunk. The relay ez' serves to close the battery circuit ofthe relays zz and cz. The relay cz is a circuit shifting or change overrelay which changes over the group selector from its selecting to itstrunk hunting or ktesting function. The relay zr is a release relaywhich closes the release circuits of the selectors when the subscriberreplaces his re'- ceiver on its switchhook.

The relays zz and cz are energized in the periods of time during whichthe armature of the line control relay travels from one extreme positionto another.l The relays zz and cz are energized by openingcontacts 232and 233 and thereby opening paths of low resistance by which they areusually short-circuited. For this reason the battery circuits of theserelays must be closed before the selecting impulses commence actuatingthe line control relay 280. This closure is effected by the contact 220of the relay er.

On the calling line being extended to the trunk line we, @172,100.2 theline control relay 280 is immediately energized by a current flowingfrom the negative pole of B1 through the lower winding of 280, obz, wb,214, bb 121, 142, bb, bbl, bb, blz, S12, 12a, au, ba, bal, oa, 141, 119,m1, 215, wa, m1 upper winding of 280 to earth.

Just before the energization of relay 280 the relay c1' was energized bya current iiowing from the negative pole through 220, 232, or to earth.In attracting its armature the relay er lets the sprin 236 press a ainstthe contact spring 237. n the energlzation of the relay 280 the relay isshort circuited by contact 233 and allows its armature to dro backwhereupon the negative battery pole 1s' momentarily connected to thechange over circuit 290. This circuit is, however, still open at thecontact 238 so that so far no shifting of circuits will be caused byapplying the negative battery pole to the wire 290 belonging to thechange over circuit.

`When the relay 280 is energized the relay w' is energized bythe openingof its short circuit at contact 232 the current flowing through 'rr fromthe negative vpole through 220, 1'7, 233 to earth.

As the calling subscriber desires a connection with subscriber No. 3465he will work his switch controller in a well known manner so as to rstcause three openings of his line loop in rapid succession. This willcause three oscillations of the armature of the line control relay 280.During these .oscillations the relays w' and 01' are short circuitedonly for very brief moments for the contacts 232, 233 are adjusted so asto be closed only whenever the armature of 280 has moved to its utmostlimit. These brief short-circuitings of the relays w andV 07' are notsuliicient for these relays to allow their armatures to fall back sothat they keep then attracted.

Each time the armature of 280 drops back a current impulse is sentthrough the vertical magnet 246 of the up and around group selector fromthe negative pole through 220, 231, 234, 224, 246 to earth. The verticalmagnet 246 lifts the wipers of the group selector, which will be assumedto be `of the Strowger type, to its third row of fixed contacts.

After the three thousand selecting impulses have thus been sent in bythe three rapid openings of the calling subscribers line loop this loop'remains steadily closed for a while until the subscriber sends in thenext series of impulses for selecting` the wanted hundred. The steadyclosure of the line loop causing an attraction of the line control relayarmature and the change over relay va relay 249. circuit 295 is shiftedfrom the vert1cal magcfr will then be short circuited long enough tocause to release its armature. .During the falling of this armature thecontact springs 237 and 291 will be connected for a moment.

.When the armature of or has fallen entirely normal switch 238, which isclosed whenthe wipers are lifted out of their normal position, 226, 247to earth. This energizes the rotary magnet 247 which turns the wipersga, gb, gc of the group selector round one step and thereby causes therotary olfnormal switches 255 and 256 to be closed. The switch 256connects an interrupter 257 to the rota magnet so that impulses nowcommence owing from the negative pole through 257, 256, 229, 226, rotarymagnet 247 to earth and the rotary magnet causes they brushes to travelover the sets of fixed contacts connected to trunks oob, @53, o0, untila trunk leading to an idle second group selector GW is reached when acurrent will flow from the positive battery pole through,

the test relay 248, test wiper gc, oe3, 300to earth.

The test relay 248 and the release relay 300 of the second groupselector both attract their armatures. The former opens its contact 229and thus interrupts the circuit of the motormagnet 247 and by itscontacts 226, 227 it also shifts the change over circuit 290 from therotary magnet to The stepping or measuring net 246 to the brush ga theconnection to the brush ga being made through contacts 225 and 270.

By its contact 228 the test relay 248 short circuits va part of itswinding and thereby reduces the potential on the test co3 to such anextent that no other first group selector will be able to establish aconnection with the second group selector^GWH.

An idle group selector in the third thousand group now being selectedand found the calling subscriber proceeds to select the desired fourthhundred group by causing four interruptions of his line loop with theaid of his switch controller. This causes four oscillations of the linecontrol relay until this subscriber in respondin After the callingsubscriber has caused the series of four interruptions of his line loopanother interval ensues during which the loop is steadily closed and theline control relay armature is steadily attracted. The change over relaycr is then steadily short circuited by the contact 233 of the linecontrol relay and allows its armature to drop back and to close thechange over circuit Awhich may be traced from the negative' pole through220, 230, 237,236, 291, 29o, 233, 227, relay 249 to earth. The relay isenergized and sends a change over impulse from the negative pole through252, 296, 277, gb, laba, 312, 313, 310, rotary lmagnet 306 of the secondgroup selector GWII to earth. The rotary magnet immediately turns thebrushes ga, gb, gc one step and thus causes the opening of off-normalcontact 313 and the closing of oi-normal contact 315. The impulse sentover the wire @b3 thus causes the immediate opening of the change overcircuit 296, 277, gb, @b3 etc. at the contact 313 and the closure of anindependent circuit for the rotary magnet by thecontact 315.

When the change over relay 249 was energized it not only closed thechange over circuit but also the circuit of a Slow-acting relay 250(negative pole, 253, 250 to earth). This relay closes a contact 254 andwhen on the immediate opening of the change over circuit 290, the relay249 is deenergized, the ringing current source 268 is applied 'through258, 254, 251, 296, 277 to the line uba until the slow-acting relayallows its' armature to fall back so as to cut oli the ringing currentat its contact 254. Although the ringing currentis applied to the linevb, no ringing current will flow because the change over circuit from296, 277, gb, fvbs, 312, 313, 310, 306 to earth was interrupted themoment the relay 249 attracted its armature and sent an impulse magnet306 causing the. contact 313 to be opened in the manner alreadyexplained.

The circuits are so arranged that a closed circuit through which ringingcurrent will flow uponthe ringing machine being applied through 296 tothe line @b3 will be found only after the inal selector (connector) hasmade connection with the wanted line and has found this line idle. Underthese circumstances the ringing current machine will send ringingcurrent to the called subscriber to the call removes his receiver fromits switchhook ,and thereby causes the ringing current to bestrengthened suiciently to energize a relay 264 at the group selectorwhich then causes the ringing current to be cut o and the 4 calling andcalled ends of the talkin circuit to be connected together by a relay 23.

In the known circuit combinations f or au. -tomatically stopping theflowing of ringing' through the rotary= current the application ofringin current to the wanted line is made depen ent on the test relay.of the final selector or connector. According as the wanted line is idleor busy the test relay will cause ringing current to be applied to it ornot..l If it were desired with circuits of this kind to place theringing current source at a group selector some special circuits wouldhave to be provided by which the influence of the test relay at thefinal selector is transmitted back to the group selector in order toconnect the ringing current to the wanted line.

By this invention these special circuits for reacting from the testrelay of the final selector upon the means at the group selector forconnecting the ringing current are avoided. According to this inventionthe ringing current is applied momentarily to the line which is beingextended to the wanted subscriber at each change over impulse.` Thepermanent connection of the ringing current y to the line is, however,made dependent on disconnecting of thev tentatively applied ringingmachine 268 is effected by the dropping back of the armature of theslow-acting relay 254 shortly after the closure of the circuit of therotary magnet 306 of the second group selector GrW,Il because on accountof the opening of contact 313 no closed circuit exists in which aringing current can `flow from the ringlng machine. The circuits bywhich the ringing machine is steadily -connected in the case of beingapplied to af'closed circuit will be explained later.

The rotary magnet 306 which is energized by current impulses from thenegative pole through 314,v 315, 310, 306 to earth turns the wipers g,g", gc of the second group selectorcausing them to brush over sets ofthe fixed bank contacts leading to the fifteen two-way switches VSthrough trunks am, bm, 08,0 until anidle trunk is reached.

a tru aizo'o, baoo @soo is ldle the twovlfa'y switch Figs. 3 and4 4associated therewith will be in its normal position and its contact 130will be closed.

The trunk am bm, 0300 to which the group selector G I extends l theconnection of the calling subscriberwill, of course, lead to a diferenttwo-way switch than the one whose brushes are connected to the callingline. But as the circuits of all the two-way switches are alike theevents which' take place at this stage of the connection lll lll

of the calling subscriber may be explained with the aid of Figs. 2, 3,4.

The two-way switches of the selected hun` dred group which are alreadybeing used for other connections will appear busy to the hunting groupselector on account of their switches 130 being open. The moment thebrushes of the group selector strike a free trunk a current will fiowthrough the test relay p1', from the negative battery pole through 301,prz, gc, 0300, converging relay SR of the idle two-way switch in thedesired hundred group, closed switch 130 to earth. The relays p1, and SRare both energized. The former opens the circuit of the rotary magnet306` at its contact 310 and by closing its contact 309 it short circuitsa part of its winding and thus lowers the potential on the test wire0300 so as to render the seized trunk busy. By closing its contacts 308,311 the test relay p1', extends the talking circuit was, 9b, tothetwo-way switch Figs. 3 and 4..

The converting-relay' SR by shifting its armature contacts converts thetwo-way switch from'a line finder to a nal selector. By opening itscontact 111 and closing the contact 112 it disconnects the starting wireSW from the seized two-way switch and extends it to the wire SW1 leadingto the next two-way switch in the hundred group so that the next callarising in this group will be assed on to thisv next two-way switch. Byclosing its contact 113 the con verting relay connects the change overwire bam, to the change over devices 190, 19.5 which at a later stagechange the connecs tion of the selecting wire a300 from the tens orsecondary motor magnet ZM to the units or primar motor magnet EM of thetwoway switc By the closure of contact 114 the selecting wire a300 isconnected to the. tens magnet ZM 1gthrough 139, 160, 158, ZM, 159 toearth). y opening of contact 115 the circuits of magnets ZM and EM whichare ordinarily connected lto the common wire 193 leading from theinterrupter 168 are separated so that ncw each of these motor magnetscan be controlled separately. At the contact 116 the release wireleading to the associated selector finder or group selector is broken inorder that when this wire is earthed on the breaking down-of theconnection in the manner to be described switch are moved into congized.At contact 118 the battery lead from the interrupter 168 to the wire1641s disconnected in order to prevent impulses flowing through 118,164,135, ha, 200, 203 to the starting relay 205 of the selector finder HS onthe shifting of the switch CS1 which happens when the two-way switch ismoved out of its normal position. The contact 107 opens current pathfrom the selecting wire a300 through 139, 131, 164, 135, 200 to thestarting relay 205 and at contacts 119, 121, 123, the lines vwl, obl,fue, leading to the selector nder are disconnected. Through contacts120, 121 the talking wires in the two-way switch are disconnected fromthe selector finder and connected to the trunk extending from the lastgroup selector in the partly established connection of the callingsubscriber.

By the opening of the contact 124 the ordinary circuit of the test relayt7' is broken and this relay is converted by the opening of they contact125l and closure of contact 126 intc a test relay for testing thecondition of the wanted line thatwill presently be selected by thetwo-way switch. By closing the contact 127 the converting relay SRcloses a locking circuit for itself which is independent of the switch130. Finally the converting relay SR moves on being energized thecontact spring 129 but in'so doing no connection is made between thecontacts 129, 128. These contacts are closed only when the r`elay SR isdeenergized and they then cause the energization of a release relay rZas will be more fully described later. The contacts 116, 129, 128 are soadjusted that the contact 116 is closed only after the contact between129, 128 is opened so as to prevent an impulse flowing from\ earththrough 128, 129, 195, 116, 217, 202 to the rotary magnet206 of theselector inder.

lVhen the converting relay SR is energized and has produced the circuitchanges just described the calling subscriber sends in the tensselecting impulses by causing a number of interruptions of his line loopthat corresponds to the tens digitof the wanted line which in this caseis 6. line control relay 280, Fig. 6, lets its armature execute sixoscillations. Each time the armature falls back an impulse flows fromthe negative battery pole through 220, 231, 234, 295, 225, 27o, ga,wwwa', gla, am, 114, 139, 158, tens motor magnet ZM, 159 to earth. Bythese six impulses the set of brushes bal, bbl, bc1 of the two-wayswitch is stepped round to the sixth set cz which is connected to thesixth ybrush seti. e. the set of brushes ba, bb, bc, that travels overthe contact sets los in the sixth row or sixth tens group. The desiredtens group is now selected. l

The

In order to select thea individual line in I the selected group of tenlines all the brush ZW is moved out of its normal position..

sets ba, bb, bc of the two-Way switch are moved five steps. The sixthbrush set ba, bb, be will then rest upon the fifth set of bank contactsin its contact row this being the set of bank contacts that belongs tothe Wanted line N o. 3465. The desired line is now selected.

The other nine sets of brushes ba, bb, bc Will also each be resting onthe fifth contact sets lcs in their respective rows, but these brushsets have no connection with a brush set bal, bbl, bol so thatthey donot establish any connection with the subscribers lines on which theyare resting.

A detailed description ofthe switching functions which take place insetting the brushes bca, bb, bo of the. two-Way switch onto the desiredline Will noW be given;

After the series of tens selecting impulses is sent in the callingsubscribers loop is again steadily .closed and the steady shortcircuiting of the change over relay 0r caused hereby results in thefallingback of the change over relay armature. A change over impulsethen ows from the negative pole through 220, 230, 237, 236, 291, 238,290, 227, relay 249 to earth. The relay 249 attracts its armature andcloses a circuit eX- tending from the negative pole through 252,

296, 277, gb, lvb, 311, glb, bm, 113, Fig. 4,

152, change over relay 190 to earth. The change over relay is energizedand immediately opens the change over circuit at ff 152 so that theringing machine 268 applied to the change over circuit through 254, 251can not send out any ringing current and Will be cut off again by thedropping back of the armature 254 of the slow-acting rela llhe changeover relay 190 closes a locking circuit for itself from the negativepole through 151, 153, 190 to earth. The switch 151 is closed When thesecondary finder.

At its contact 139 the change over` relay separates the selecting Wirea300 from the secondary motor magnet ZM and connects it through contact138 and through 196, 162 to the primary motor magnet EM.

On the calling subscriber noW sending the five units selecting impulsesthe armature of the line control relay 28() drops back five times and veunits selecting impulses iiow through 220, 231, 234, 295, 225, 270, gtr,/v3,308, gla, a300, 114, 138, 196, 162, primary motor magnet EM, 163 toearth, these impulses causing the brush sets ba, bb, bo to be moved tothe fifth bank contact sets and to Aselect the desired subscribers linein the manner already described.

After the last series of selecting impulses has gone in the line controlrelay 280 keeps its 'armature steadily attached so as to deenergize thechange over relay c1' again by short circuiting it. 'The relay 249 isthenl momentarily energized and a test impulse Hows from the negativepole through 252, 296, 277, gb, aba, 311, gib, baco, 113, switch 150which is closed the moment the primary linder is moved out of its normalposition, 149, rela 193 to earth. The relay 193 is energize and byopening contact 149 disconnects itself from the change over Wire bm. Butit also closes a. test circuit extending from the positive pole through198, 146, 147, relay t1', 126, cv, bel, bc, test Wire 03,65 (not shownin the drawing but similar to the test Wire of the calling subscriber)cut ofi' relay c7' of the desired line No. 3465 to the negative pole ofthe exchange battery. If the Wanted line is free the relay t1', whichnow acts as a test relay, will be immediately energized and will extendthe lines a300, bw, to the line of the Wanted subscriber by closing itscontact 141, 142. The ringing machine, which is applied by the contact254 of the slow-acting relay to the line bm after the change overimpulse sent through contact 252 ceases, now sends out a ringing currentbefore the Slow-acting relay lets its armature drop back. The ringingcurrent liows from the earth through 268, relay 258, 254, 251, 296, 277,gb, bbs, 311, g-lb, bm, 121, 142, bb, bbl, bb, bm, aiebb, bell of-Wanted subscriber No. 3465, 3465a, c3465, ba, bal, aa, 141, 120, a300,gla, 308, aaa, ga, 270, 225, 295, 298 to earth.

By the immediate iiowing of the ringing current the steady connect1on ofthe same to Wanted line is effected by means of a relay 258 Which isenergized by the ringing current and closes a ringing current path whichis independent of the contact 254 of the slow-acting relay, this pathleading through 259, 260, right hand Winding of relay 299, 296, 277 tothe above-described ringing circuit. The relay 299 is now energized andthe circuit including relay -258 is broken at 260 which causes the relay258v to open its armature contact 259 and to permanently disconnectitself.

The yringing current is now kept connected to the wanted line by therelay 299 `Which closes the contacts 261, 262 before opening the contact260. If the interrupter 267 which is continually running just happenedto have closed its contact 265 the ringing current will flow from 268through 265, 264, 261, right hand Winding of 299, 286, 277 to the Wantedsubscribers ringing circuit. But if the interrupter happens to haveclosed the contact 266 at the moment the relay 258 is cut off, theringing current will not liow through the line of the Wanted subscriber'but through 266, 263 and the left Winding of 299. It: is thus seen thatin any case the one or the other Winding of 299 is energized. If thecontact 265 is closed the ringing current flows through the relay 264and the right hand winding of 299 to the wanted line,but if the contact266 is closed the whole ringing current flows through the left windingof 299 and` there will be a pause in the ringing of the wantedsubscribers bell.

When the called'party responds by removing his receiver from hisswitchhook the ringing current ilowin through the relay 264 isstrengthened su ciently to cause'this relay to close its armaturecontact 263. A current then flows from the negative pole through 263,connecting relay 273 to earth. The relay 27 3 thereupon interrupts theflow of ringing current at 277 so that the energization of the rightwinding of 299 ceases before the left winding is reenergized. The relay299 is therefore deenergized and the ringing machine 2'68 is cut o at261, 262.

By closing its contacts 271, 276 the relay 273 extends the line of thecalling subscriber to that of the called subscriber and discnnectsselecting and change over circuits at contacts 270 and 277.

The relay 273 closes a locking circuit for itself by its contact 272(negative pole, 255, 272, 273, earth) and by its contact 269 itmomentarily short circuits a part of the winding er and thus momentarilystrengthens the current in the meter circuit (vez, v01, 123,143, ce,601, be, cl2, 2,2, .negative pole) so as to make the meter 2,2 attractits armature and register the conversation.

In order to cause the meter circuit to be only momentarily closed by theenergization of the relay 273 so as not to impair the busy condition ofthe test wire fue, the contact 269 is'made like the contact 119, 120 ofthe call regulator AR, Fig. 2. This is more clearly shown in Figs. 8 and9. In Fig.v 8 273 represents the end of the armature that is moved inthe direction indicated by the arrow 274 when the relay 273is'energized.

` The end of the armature is round. and glides along the right handoblique surface at the end of the. contact spring 269 so as to move 269towards the left and against the contact spring 269. When the armatureis fully attracted its end will be located above269 as indicated by thedotted circle 273". On the deenergization of the relay 273, the roundend 27 3' glides along the left side of the oblique end of 269 forcingit further away from 269 instead of towards 269. -The aecting of thebusy condition of the line ce, can also be 4prevented by using a contact119, 120 which causes the momentary closure of the meter circuit on thedeenergization of relay 273 at .the finish of the talking connection. Inthis case a similar arrangement to that illustrated in Figs 8 and 9 isused, butthe end-of the armature is arranged so as to push the spring269 away rom1269 when it is attracted and to push it against 269 when itfalls back. In other words the end of 269, instead ofrun- 271, 2 6 acircuit is closed including the relays 278, 279 and extending from earththrough 278, 271, ga, was, 308, glo., a300 to the two-way switchy whichhas established the connection with the wanted line, 120, 141, wa, bal,ba of the sixth set of brushes, 07348 346m, Sms, 34651, 63,65, bb,661,96, 142, 122, 6300, glb, 311, lcbm gb, 276, 279 to the negativepole. The relays 278, 279 are excited; 279 closes its armature contact240 and 248 opens its contact 239.

The calling subscriber is now connected to the. called subscriber overthe following path: S12, 12a, au, ba, ba.1 of the two-way switch whichhas connected to the calling line, bal, ca, 141, 119, 215, wa, fvaz,co1, 271, geni/vas, 308, gla, a300, two-Way switch VS in the calledhundred group, contact 120 of the convertin relay SR of this switch,141, oa, bal, ba o the sixth set of brushes of the two-way switch,c3465, 3465a, Sms, 34656, 634,5, bb, 661, lvb, 142, 122, 6,00, glb, 311,cbs, gb, 276, co2, wb2, wb, 214, '061, 121 of the twoway switch that hasconnected to the calling line, 142, fvb, bb1 6b of this switch, 612,12b,

If the calling subscriber is the first to terminate the connection byreplacing his receiver on its switchhook and thereby opening his lineloopl the line control relay 280 will be deenergized and the releaserelay W' will be steadily short circuited. The latter relay will thenallow its armature todrop back and close the release circuit (earth,235, 245, 223, negative pole). The release magnet 245 will be energizedand will cause the first group selector to be restored to its normalposition. The release magnet also opens its armature contact 222 andthereby deenergizes the relays er and pril.. The

relay pril, lets its armature drop back, thus opening its lockingcircuit at its front contact 212 so that, until the starting relay 205is energized again, no reenergization of the relay prh can take place.By the contact 210 the circuit of the rotary magnet 206 of the selectorfinder is closed (negative pole,

cuit extending :from earthl through 209, 202,

217, al, 116, 195, relay rl to the negative pole. The release relay rlof the two-way switch is thus energized and closes a .locking circuitfor itself which may be traced from the negative battery pole to TZ,137, 107 `to earth. At its contact 136 the release relay opens thelocking circuit of the relay tr. This relay is then deenergized andcloses at its back contact 131 the circuit of the magnet EM (negativepole, 168, 108, 155, 118, 157, 131, 115, 162, EM, earth) which remainsclosed until the driving device Dof the primary linder reaches itsnormal position and disconnects the interrupter 168 from the motormagnet EM by opening the contact 108.

The motor magnet ZM of the secondary finder is completely disconnectedfrom the circuit of the motor magnet EM of the primary finder at contact1951 of the restoring relay TZ in order that the two iinders may moveindependently of each other into their normal position.

The independent restoring circuit of the motor magnet ZM is closed bythe contact 1961 of the restoring relay l'Z and extends from thenegative pole to interrupter 1971, 1961, 1671, ZM, 159 and to earth. Themo- I ment the secondary-finder reaches its normal position the contact1671 is opened and the motion of the finder is stopped through.

the interruption of the circuit of the magnet ZM.

In order to prevent interruptions of the circuits of the magnets EM, ZM.by enerizations of the test relays pr, sr caused during the travel ofthe brushes pb, sb into their normal positions by their striking earthedguide wires the battery lead to these relays is kept open by the contact134 of the restoring relay rl until this relay is deenergized. Therestoring relay is, however, not deenergized until the two-way switchreaches its normal position and opens the locking circuit of therestoring relay rl by severing the contacts 107 and 167.

To prevent the flowing of impulses from 168 through 108, 155, 118, 156,164, ha, 200 to the startin relay 205 when the relay pril, is deenergizeand the-contact 200 closes the armature contacts of pff-h are soadjusted that 200 remains open until shortly after the closure of 217 i.e. until shortly after the energization of rl and until the opening of135 by rl. By this means current impulses are prevented from flowingfrom 168 through 108, 155, 118, 156, 164 to the starting wire hav duringthe restoration of the two-way switch which would cause a displacementof the selector finder HS.

The second group selector GrVVII is releasedv closes the circuit of therelease magnet 304 (negative pole, 302, release magnet 304, 303,

earth) which thereupon releases the second group selector. At the momentthe release circuit is closed the test circuit p72 is opened at 301 soas to prevent any energization of the test relay pr2 whilst the brushg1@ travels over the bank contacts of other trunks 0300 during therestoration of the selector.

The moment the contact arm g1c of the second group selector leaves thetrunk 03,0 leading to the called'hundred group the converting relay SRof the two-way switch in this group that was used for the talkingconnection is deenergized and on its armature falling back the contact128, 129 is momentarily closed. This causes the energization of therestoring relay rl associated with this two-way switch, the restoringcircuit extending from earth, 128, 129, 194, rl to the negative pole.

The deenergization of the converting relay SR results in the opening ofthe circuit i of the test relay t1' (earth, 140, tr, 126, v0, 501, bc,03465, @T3465 by the contact 126.

The two-way switch used Jfor establishingA the connection with thewanted subscriber 4is now restored in the same manner as the two-wayswitch that connected to the calling line, the restoring functions ofwhich have already been described.

It will be remembered thatv the magnet EM is energized by impulses fromthe negative pole through 168, 108, 118, 157, 131, 115, 162, EM, 163 toearth and that the Vmagnet ZM receives its restoring impulses from thenegative pole through 1971, 1961, 1671, ZM, 159 to earth.

If the called subscriber is the first to replace his receiver on theswitchhook at the end of the conversation the restoration of theswitches, selectors etc. will be initiated by the deenergization of therelays 278, 27 9. The rela 279 is slow-acting and lets its armature ropback later than the relay 278.

The deenergization of these two relays Lwill thus result in a shortclosureY of a release c1rvthe restoration of the switches in theconnecment the two-way s'vitch is set onto thewanted line the relay trwill not be energized nefasta as previously described and hence thetalking i leads of the calling subscriber will not be connected 'throughthe contact 141, 142' to the line of the wanted subscriber.

A feature of the meter circuits used in the present system which was notmentioned in the above description will now be' pointed out:

It was shown that the actuation of the meter of the calling subscriberis caused by strengthening the current flowing in the wire 012, thisstrengthening being produced by partially short circuiting the windingof relay er by means of contact 269. Now when a two-'way switch is usedtdestablish a connection with a wanted line, the energization of therelay t1 of this switch and the partial short-circuiting of this relaywill also produce'a strengthening of the current in the wire cM of thecalled subscriber. But the alteration of the current strength will bebalanced by the resistances who, wm so as to prevent the calledsubscribers meter being actuated.

Mention will now be made of a detail regarding the ringing and changeover circuits:

It will be remembered that the change over relay 249 is deenergized fora moment at the end of each series of selecting impulses and momentarilyconnects the negative pole through 252 and 277 to the change over wire.Immediately afterwards, on the dropping back of the armature of 249,tthe ringing current machine 268 is connected through 254, 251, 277 tothe change over wire, but a current does not flow through it because thecontact 313 is immediately opened by the operation of the rotarynmagnet306. But it is possible that the group selector GLWII will find thefirst or second trunk a300 idle and that in such a case the .test relaypf2 will very soon extend the change over wire 'U63 to the linal two-wayswitch by closing the contact 311. This ex-l tension of the-change overwire would then possibly take place `before the. slow-acting relay 250reopens its contact 254 and disconnects the ringinglnachine. Thiswouldresult in the steady application of the ringing machine to thechange over circuit because a ringing current would flow from earththrough 268, 258, 254, 251, 296, 277', gb, fvba, 311, 911), 5300, 113(this contact would be closed by the energization of SR) 152, 190 toearth. In order to preventthis undesirable iowing of ringing current4 arswitch is preferably provided at the point 1991 indicated by the crossin the two-way switch which is closed only when the calling subscribercommences to send inhis tens selecting impulses. By that time theslowacting relay 250 will be lsure to have found time to open itscontact 254. The switch at point 199 may consist of a contact compris-.to their normal idle condition.

ing two springs similar to 167 which closes the moment an impulse issent through the tens magnet ZM.

It was assumed in the case of the above connection between a calling anda called subscriber that Ia two-way switch that is lassociated with aselector finder extended the calling subscribers line to a first groupselector. If, at the time the calling subscriber makes a call, the nextidle two-way switch in the group is one that is connected directly to athe establishment of the connection between the calling and calledsubscribers will be as described above except that the functions of theselector finder will 'be omitted. The lines fm1, fvbl, 'v01 will in thiscase not pass through contacts 214, 215, 216 and brushes wa, wb, wc butwill be directly connected to an associated first group selector and thestarting wire extending from point 157' through 135 will rbeunnecessary.

The release wire al instead of vpassing through contact 217 will beconnected directly to an armature contact of the release magnet 245 ofthe lirst group selector and on thev` energizatio'nN ofthe releasemagnet thel restoration of the two-way switch will be initiated by thee'arthing of the restoring Wire al.

Another point will be mentioned in connection with regulating of theincoming calls by the call regulator. It will be remembered that thecall regulator ordinarily prevents two calls from being simultaneirstgroup selector, all the events in ously passed on to the two-wayswitches of a hundred group. The call`regulator will perform itsfunction perfectly as long as not more than two calls come in at thesame or almost the same instant: This will generally be all thatisrequired ina practical system. That three or more calls Will come inat the same instant is almost out of question, Even this contingency canhowever be provided for by arranging a special relay common to eachgroup of subscribers which will be excited if more than one subscribercalls in the interval of about a second during which a twou way switchis in the act of making a connection with a calling line. vThe specialcommon relay will th n cause relays, of which one is associated witheach of the lines that .happens to call in the above mentionedinpossibly causing ineffective line' finding op-v erations of thetwo-way switches. The

special signal would cause the subscribers who sent in simultaneouscalls to hang up their receivers and to thus restore their lines Thesubscribers would then wait a few seconds be-

